Helcionopsis is an extinct genus of paleozoic monoplacophora

Monoplacophora

Monoplacophora, meaning "bearing one plate", is a polyphyletic class of mollusks with a cap-like shell, living on the bottom of deep sea. Extant representatives were unknown until 1952; previously they were known only from the fossil record.- Definition :...

n in the family Tryblidiidae

Tryblidiidae

Pilina is an extinct family of paleozoic monoplacophorans in the superfamily Tryblidioidea.- Genera :Genera in the family Tryblidiidae include:* Tryblidium Lindström, 1880...

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The generic name is from the external resemblance which the genus bear to the recent species of the genus Helcion

Helcion

Helcion is a genus of sea snails, the true limpets, marine gastropod mollusks in the family Patellidae.-Species:Species within the genus Helcion include:Subgenus Ansates : accepted as Ansates G.B...

in family Patellidae

Patellidae

Patellidae is a taxonomic family of sea snails or true limpets, marine gastropod molluscs in the clade Patellogastropoda.Patellidae is the only family in the superfamily Patelloidea...

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Species

Species in the genus Helcionopsis include:

• Helcionopsis radiatum
  Helcionopsis radiatum
  Helcionopsis radiatum is an extinct species of paleozoic monoplacophoran in the family Tryblidiidae.This species was first named as Tryblidium radiatum and described from Silurian in crystalline limestone of Wialmsudd near Fårösund in Sweden by Gustaf Lindström in 1884. Lindsröm found only one...
  
  (Lindström, 1884)
• Helcionopsis reticulatus
  Helcionopsis reticulatus
  Helcionopsis reticulatus is an extinct species of paleozoic monoplacophoran in the family Tryblidiidae....
  
  Easton, 1943
• Helcionopsis striata
  Helcionopsis striata
  Helcionopsis striata is an extinct species of paleozoic monoplacophoran in the family Tryblidiidae.- Shell description :The shell is rather strongly convex, acuminate-ovate in outline, broadly and regularly rounded behind, pointed in front where the apex projects slightly beyond the margin of the...
  
  Ulrich, 1897
• Helcionopsis subcarinata
  Helcionopsis subcarinata
  Helcionopsis subcarinata is an extinct species of paleozoic monoplacophoran in the family Tryblidiidae.- Shell description :The shell is small and subovate in outline. The anterior and posterior margins are subequal and sharply rounded in the middle. In the cast the apex is depressed, small and not...
  
  Ulrich & Scofield, 1897

Shell description

General form and position of apex

Apex (mollusc)

Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...

 is as in Tryblidium

Tryblidium

Tryblidium is a paleozoic genus of Ordovician and Silurian monoplacophorans.The generic name comes from the Greek , which means patella.- Species :Species in th genus Tryblidium include:* Tryblidium acutum* Tryblidium arctica...

, from which Helcionopsis differ in having the surface marked by fine radiating striae. Muscular scars of this genus Helcionopsis unknown in 1897, when the genus was described.